CARBONATE BLEND POLYMER COMPOSITIONS COMPRISING A HIGH MOLECULAR WEIGHT BRANCHED CARBONATE POLYMER COMPONENT AND METHODS FOR THEIR PREPARATION

Abstract: Novel carbonate polymer blend compositions and processes for their preparation are disclosed where an amount of a high molecular weight branched carbonate polymer component (HMWB PC) is combined with a second, homogeneously dispersible lower molecular weight polycarbonate. A preferred aspect of the invention is directed to intermediate compositions and processes for their use where the second PC is combined with a HMWB PC precursor having latent thermally reactive moieties which can be activated to produce a desired and controlled level of high molecular weight, branched carbonate polymer component. Arylcyclobutene moieties are found to be preferred latent thermally reactive moieties. The carbonate polymer blends according to the present invention have surprisingly improved combinations of physical properties, thermal stability, color, melt strength, transparency and processability. When shaped or molded into various types of articles, the articles posses these very desirable properties and are additionally able to be provided with a low gloss or matte surface. These polymeric compositions are well suited for use in preparing molded articles, such as injection molded articles; composite or blend materials with further filler or blend components; extruded articles such as sheet, fiber or film; and blow molded or thermoformed articles.

Description: CARBONATE BLEND POLYMER COMPOSITIONS COMPRISING A HIGH MOLECULAR WEIGHT BRANCHED CARBONATE POLYMER COMPONENT AND METHODS FOR THEIR PREPARATION This invention relates to novel carbonate polymer blend compositions comprising two carbonate polymer components. As first component, the blend comprises an amount of a 5 high molecular weight, branched carbonate polymer component ("HMWB PC"). As second component the blend comprises an amount of a lower molecular weight carbonate polymer. According to a preferred aspect of the invention, the high molecular weight component is homogeneously dispersible, preferably soluble or miscible therein. The invention also involves an improved intermediate blend composition for preparing such compositions which 1 u intermediate composition comprises a precursor for the first component. This precursor is a carbonate polymer having latent thermally reactive moieties which can be thermally activated to produce a desired and controlled level of high molecular weight, branched carbonate polymer component. Improved carbonate polymer blend compositions are very easily prepared when • -- * the precursor for the first carbonate polymer component is combined with an amount of a second carbonate polymer and the latently reacti e moieties are thermally activated to produce a high molecular weight, branched carbonate polymer component. These polymeric compositions are well suited for use in preparing molded articles, such as injection molded articles; composite or blend materials with further filler or blend components; extruded ** • *- ■ articles such as sheet, fiber or film; and blow molded or thermoformed articles. It is known that articles prepared from a carbonate polymer ("PC") having a higher molecular weight (Mw) possess generally better physical properties than if molded from a lower molecular weight carbonate polymer. Unless otherwise indicated, the references to "molecular weight" herein refer to weight average molecular weights ("Mw") determined on -* • --' the carbonate polymers using gel permeation chromatography with a bisphenol A polycarbonate standard. Otherwise, viscometry or light scattering can also be used to determine weight average molecular weight. It should be noted that various references. including several that are discussed below, refer to "viscosity average" molecular weight, which is not the same as weight average molecular weight but can be correlated ::r converted 3** 1 to Mw values. It is also known that the higher the molecular weight of the carbonate polymers, the more difficult they are to process due to their higher viscosity and corresponding lower melt flow rate. See for example Japanese Patent Publication 03-243,655 (1992) where amounts of a lower molecular weight carbonate polymer are incorporated into a high molecular -* •* - ■ carbonate polymer composition in attempting to improve the flow and processability properties of such carbonate polymers. However, it is known that the separately prepared higher and lower molecular weight components are difficult to homogeneously blend due to their difference in melt viscosities and do not produce the best possible combinations of polymer processability and molded part physical properties. It is well known that branched carbonate polymers are commercially available and are known to have greater melt strength and be more shear sensitive in the melt phase than linear polycarbonates. Therefore, the branched polycarbonates are known to be better suited for some uses such as blow molding or thermoforming. In Japanese Patent Publication 60-215,051 (1985), it is shown that branched resins can be incorporated in varying amounts into blends with a high melt flow rate (low molecular weight) linear carbonate polymer to improve the melt strength of the low molecular weight resin. It is also known that additives, such as Teflon polytetrafluoroethylenes, can be added to polycarbonates to provide an increase in melt strength but have drawbacks such as loss in transparency and toughness. In U.S. Patent 4,912,914 it is proposed that crosslinked or branched polycarbonates can be prepared by incorporating a diester diphenolic monomer into the carbonate polymer backbone, then heat activating the crosslinking reaction. However, since the crosslinking reaction causes the polymer backbone to be cut at the point of crosslinking, the polymers that are taught would be expected to have undesirable levels of low molecular weight polymer byproducts and high molecular weight or crosslinked gel byproducts due to the random and uncontrollable crosslinking. These polymers would also be expected to have higher color levels and reduced hydrolytic stability. In U.S. Patent 3,770,697 and U.S. Patent 3,652,715 carbonate polymers are provided with thermally activated, terminal or pendant unsaturated imido groups. These functioπalized, curable polymers are then taught to be employed independently or in mixtures with other monomers or polymers, as molding compounds, films, and laminates. A cast film that was prepared from a blend of an imido-functionalized carbonate polymer composition and an amount of standard, non-functionalized polycarbonate and reacted using an additional chemical initiator compound showed an increase in heat resistance. It has been found, however, that the molecular weight of these products is unstable and that the products have an undesirable discoloration. It has also been found, unfortunately, that such unsaturated imido-functionalized carbonate polymers are not readily produced in interfacial carbonate polymer production processes due to the nitrogen-containing imido groups that must be incorporated. In addition, the initiation and reaction process requires relatively long reaction times. It istherefore a goal of the present invention to provide improved carbonate polymer compositions which are easily prepared and possess good combinations of processability, stability and physical properties. Preferably such compositions are easily prepared from one or more components produced in an interfacial carbonate polymer process. It is also desired to prepare such compositions without having to incorporate an additional free radical initiating compound such as an organic peroxide or employ radiation techniques which can also lead to polymer decomposition. It is also desired to prepare such improved carbonate polymer blend compositions using a high molecular weight branched carbonate polymer component that can be readily mixed homogeneously into the second component while avoiding unacceptable levels of gel that detract from the balance of the desirable physical, rheological and optical properties. Therefore, in one aspect the invention is a carbonate polymer blend composition comprising a first high molecular weight branched carbonate polymer component and a second, different carbonate polymer component having a lower molecular weight than the first component, characterized in that the first high molecular weight branched carbonate o polymer component is thermally stable at a temperature at least 100°C above the Tg of the carbonate polymer blend composition. Preferably the first carbonate polymer component is prepared from a precursor component comprising a carbonate polymer having one or more latently reactive moieties capable of forming a high molecular weight branched carbonate polymer upon heat activation. 5 In another aspect, the present invention is an intermediate carbonate polymer blend composition suitable for preparing a carbonate polymer blend composition as described above comprising a precursor component having one or more latently reactive moieties capable of forming a high molecular weight branched carbonate polymer upon heat activation and a second, different carbonate polymer component having a lower molecular weight than o the high molecular weight branched component. In a preferred aspect, the precursor component comprises terminally located, latently reactive arylcyclobutene moieties. A particularly advantageous aspect of the present invention is the obtai nment of the desirable physical property combinations in an easier fashion than those described in the art. A preferred aspect of the present invention is an improved process for preparing a blend of 5 a first, high molecular weight branched carbonate polymer component and a second, lowe r molecular weight carbonate polymer component different from the first carbonate Dolyme r component comprising the steps of (a) preparing a precursor component capable of forming the first high molecular weight branched carbonate polymer component, said precursor component comprising a carbonate polymer containing latent thermally activated reactive 0 moieties; (b) combining the precursor component with the second carbonate Dolymer, and (c) thermally activating the latently reactive moieties of the precursor component to provide a generally homogeneous caroonate polymer blend composition. In a preferred process aspect, in step (b), the precursor component is combined with the second carbonate polymer component by (1 ) dry blending or dual feeding the 5 precursor component with the second, lower molecular weight carbonate polymer component and then (2) melt blending the precursor and second components at a temperature and for a time less than sufficient to significantly thermally activate the latently thermally reactive moieties and (3) recovering an intermediate carbonate polymer biend composition comprising a precursor component having one or more latently reactive moieties. According to these processes, the precursor component comprising latent, thermally activated reactive moieties is intimately dispersed throughout the second carbonate polymer prior to or in conjunction with thermal activation of the latently reactive moiety and creates a high molecular weight branched carbonate polymer component in situ. In this way, carbonate polymer components of similar initial molecular weights can be more readily blended prior to the creation of the high molecular weight branched component. This will result in a better, more homogeneous mixture of the high molecular weight branched carbonate polymer component with the other carbonate polymer component. It has been surprisingly found that although the precursor carbonate polymer component with latent, thermally reactive moieties would have a tendency to form a highly crosslinked polycarbonate gel when reacted separately, when dispersed in a carbonate polymer composition prior to the activation of such moieties, undesirably large domains of highly crosslinked polymer gels are substantially reduced and preferably eliminated insofar as they produce undesirable effects in the physical, rheological, optical or surface aesthetic properties in molded articles. In other embodiments, the invention involves ignition resistant compositions which are optionally transparent and comprise: as a first component, a carbonate polymer drip reducing additive; as a second component, a second different carbonate polymer component; arid, as a third component, other optional ignition resistance additives, wherein the ignition resistance of the blend composition, when tested according to UL 94 attains at least a V-0 rating at 1/8 inch or is more ignition resistant. Preferably, the carbonate polymer drip reducing additive is a high molecular weight branched carbonate polymer drip reducing additive which may be formed prior to or during ignition conditions. In other aspects, the invention involves improved processes for preparing fibers, blow molded or thermoformed parts, opaque parts having controlled gloss levels and transparent to translucent parts having controlled light diffusing properties. The parts and shaped articles that result are also aspects of this invention. As will be described in more detail below, the carbonate polymers according to the present invention have surprisingly improved combinations of physical properties, thermal stability, color, melt strength, transparency and processability. When shaped or molded into various types of articles the very desirable properties mentioned above are obtained. In addition, depending upon the molding or shaping method, iight diffusing anα/or surface altering effects may also be observed. In particular, the articles can be provided with a range of surface and Iight diffusing effects including transparency, translucence, high gloss, non-glare, low gloss, mottling, frosting or matte surface. A key feature in preparing the compositions according to this invention is obtaining a suitable high molecular weight, branched carbonate polymer component ("HMWB PC") which is sufficiently stable and dispersible in the balance of the carbonate polymer composition Preferably the HMWB PC is capable of providing a homogeneous mixture with the other carbonate polymer component in the claimed compositions without obtaining undesirable byproducts such as phase-separated very high molecular weight polymer, highly crosslinked gels or a very low molecular weight component and without the use of additional reactive additives such as free radical initiating compounds which can cause undesired degradation, color formation and/or uncontrolled crosslinking in the polymer composition or additives. Moreover, the use of free radical generating initiators is incompatible with the use of many of the known polymer stabilizing additives which are radical scavengers and are needed in carbonate polymers. As compared to similar types of materials that have been previously prepared or obtainable, it has been found to be imoortant that the final high molecular weight branched component for use according to the present invention be thermally stable at a temperature at least 100°C, preferably at least 125°C, more preferably at least 150°C, above the Tg of the carbonate polymer blend composition. For the types of carbonate polymers that are most likely to be used as the lower molecular weight second component, such as the commercially available polycarbonate resins based on bisphenol A, the Tg is 150°C. Likewise, where the HMWB PC is based on bisphenol A, the Tg will be in the same range and the claimed blends based on such polymers will have a Tg in this range Otherwise, where there is a difference between the Tg's of the two components that are combined and provided that the two components are sufficiently miscible to provide the homogeneous blends according to this invention, the resulting blend will have a single intermediate Tg As used herein and well known to those skilled in the art, the term Tg refers to the glass transition temperature of the polymer or blend and is defined as the inflection point on the heat flow curve as determined by differential scanning caloπmetry It is therefore one of the novel and advantageous features of this invention to provide carbonate polymer blends of this type with a HMWB PC component that is thermal I y stable during extended exposure to higher temperatures. This level of thermal stability can be determined by various known techniques such as by thermogravimetπc analysis or by the measurement of color development or molecular weight change with increasing heat Obviously, where the lower molecular weight second component (for example, a commercially available polycarbonate resins based on bisphenol A) is determined or known to be sufficiently thermally stable, thermal instability or stability of the HMWB D C can be determined based on thermal instability or stability of the blend. In particular, with regard to thermal stability, it 's preferred that the compositions according tothe present invention employ a high molecular weight branched component that maintains its molecular weight (after completion of any in situ forming reaction) upon heating in nitrogen to a temperature at least 100°C, preferably at least 125°C, more preferably at least 150°C above the Tg of tne carbonate polymer blend composition. Bythe term "maintains" .ts molecular weight, it is meant that the HMWB PC does not contribute further significant molecular weight increases or decreases to the blend, preferably none of more than 10 percent, more preferably none of more 5 percent from its initial value Preferably there is minimal color developed under these conditions, it being desirable to avoid the brown coloration that is observed when a carbonate polymer that is not thermally stable is heated to temperatures 100 to 150°C above the Tg of the carbonate polymer The high molecular weight branched carbonate polymers suitable for use as the first component in the compositions according to the present invention can be prepared by techniques known in the literature In general, these carbonate polymers are prepared from one or more multihydπc components by reacting the multihydπc compound, such as a diphenol, with a carbonate precursor such as phosgene, a haloformate or a carbonate ester such as diphenyl- or dimethyl carbonate. Aromatic carbonate polymers are preferred and aromatic diphenols are preferred for use as at least part of the multihydπc compound Preferred diphenols include but are not limited to 2,2-bιs (4-hydroxyphenyl)-propane (that is, bisphenol A), phenol, 4,4'-(9-H-fluorene-9-ylιdene)bιs (that is, bishydroxyphenylfluorene), 4,4'- thiodiphenol (TDP), 1,1-bιs (4--hydroxyphenyl)-1-phenyi ethane (bisphenol AP); phenolphthalein; bis (4-hydroxyphenyl) diphenyl methane; tetrabromobisphenol A (TBBA); and tetrachlorobisphenol A (TCBA). These carbonate polymers also include aromatic carbonate polymers prepared from two or more different dihydπc phenols or a combination of a dihydπc phenol and a glycol or a hydroxy- or acid-term mated polyester or a dicarboxyhc acid in the event a carbonate copolymer or heteropolymer is desired The high molecular weight branched carbonate polymers can be prepared from such materials by any of several known processes such as the known interfacial, solution or melt processes Suitable types and amounts of chain terminators (typically monophenolic compounds) and/or branching agents (typically phenols having three or more hydroxy groups) can be employed to obtain the desired molecular weight and branching degrees in the high molecular weight branched component. In general, by whatever production technique it is prepared, the high molecular weight, branched polymer should have a weight average molecular weight of at least 3 times that of the second carbonate polymer, preferably at least 5 times and more preferably at least 10 times In order to obtain polymer blends with minimized levels of gels and other beneficial effects of the high molecular weight branched component, it has been found that the weignt average molecular weight of the high molecular weight branched component should not be higher than 200 ti mes that of the second carbonate polymer, preferably not higher than 150 times, more preferably not higher than 100 times, more preferably not higher than 50 times When using a linear carbonate polymer based on bisphenol A and having a weight average molecular weight in the range of 10,000 to 60,000, as the second, lower molecular weight carbonate component, it has been found that the weight average molecular weight of the high molecular weight branched component should be at least 100,000, preferably at least 125,000, more preferably at least 150,000. Correspondingly, in combination with second components of these types, the weight average molecular weight of the high molecular weight, branched component is generally less than 2,000,000, preferably less than 1 ,500,000, more preferably less than 1 ,000,000. It has been found very advantageous to prepare suitable high molecular weight, branched carbonate polymer by using a precursor carbonate polymer component which has latently reactive moieties. These moieties should react with sites in the carbonate polymer or with one or more other latently reactive moieties to form the HMWB PC. These moieties can be incorporated into a carbonate polymerwhen that polymer is being initially polymerized or attached to the polymer in a later functionalization step Preferably the precursor component latently reactive moieties, when they react primarily with one another, are capable of forming products having an average functionality greater than two This means that for at least a portion of the moieties, more than two of the moieties react together and thus form branches from a polymer backbone chain. Latently reactive moieties forming products having an average functionality of two or less would produce only chain extension products without branches off the backbone. Preferably the selected latently reactive moieties can be rapidly activated, preferably thermally, without the use of additional reactive compounds at a desired point (temperature/time history) in the blend preparation process and/or in the process for preparing shaoed articles. Selection of a preferred latently reactive compound and avoidance of the additional reactive compounds produces a high molecular weight, branched carbonate polymer without producing undesired, low molecular weight byproducts or highly crosslinked polymer gels. Most preferably, such moiety can be incorporated into the carbonate polymer in an interfacial carbonate polymer polymerization process. As used herein, the term "interfacial carbonate polymer polymerization process" refers to a process where the multihydric reactants, including any multi- or mono-reactive compounds used to incorporate the latently reactive moiety, are dissolved in a water phase by forming an alkali metal adduct, then reacted with the carbonate polymer precursor forming a polymer which is dissolved in a separate organic phase. For example, dihydπc phenols are dissolved as alkali metal phenates for reaction with the carbonate precursor forming an aromatic carbonate Dolymer which is dissolved in a separate organic phase As those skilled in this area know, nitrogen-containing moieties, such as the unsaturated imido compounds of U.S. Patent's 3,652,715 and 3,770,697, cannot generally be present or incorporated in such a process and are therefore not suitable for use in this aspect of the present invention. According to a preferred aspect of the present invention, an intermediate composition is formed comprising a carbonate polymer precursor component having latently reactive moieties and a second carbonate polymer component having a lower molecular weight than the final high molecular weight branched component. Then, a high molecular weight, branched carbonate polymer is prepared without the use of added radical initiating compounds, or the like, merely by activation of the latently reactive moieties, preferably thermally. As known in the art and shown in U.S. Patent's 3,652,715 and 3,770,697, it is often necessary to incorporate reactive additives such as organic peroxides in order to initiate the reaction or addition polymerizing activity of functional moieties at sufficient rates. However, it is generally undesirable to incorporate chemicals of this type in molding resins due to the increased expense, possibility of volatile byproducts and deleterious residues. Therefore, the compositions according to the present invention, without such chemical initiator additives, offer an unexpected benefit in terms of being able to provide equivalent or better results in terms of ease of preparation, stability and performance of the resultant resins. As mentioned, in a preferred embodiment of the present invention, the latently reactive moieties are activated thermally and at temperatures and other conditions below which any of the other carbonate polymers in the blend composition are degraded. By "thermally" or "heat" activated, it is meant that the reaction of the moiety with one or more other like moieties or reactive sites will occur at a reasonable rate upon bringing the composition to an elevated temperature but will not occur at a significant rate, preferably not at any measurable or rate, at ambient temperatures (i.e., below about 60 C C, preferably below about 50°C). With regard to the temperatures which are sufficient to initiate reaction at reasonable rates, these are preferably at least the blend Tg, more preferably at least 100°C above the blend Tg, most preferably at least 150°C above the blend Tg. By "reasonable rate" it is meant that the reaction is essentially completed and the HMWB PC is thermally stable within 24 hours, preferably 10 hours, more preferably 1 hour, most preferably 0.25 hour after bringing the composition to the elevated temperature. It is also important to be able to thermally activate such latent reactive moieties under conditions and particularly at temperatures below which any of the other carbonate polymers in the blend composition are degraded. The degradation conditions for a particular carbonate polymer, of course, depend somewhat on the exact composition of the carbonate polymer, including the particular multihydroxy compound(s) upon which it is based. For example, in the case of polycarbonates based on phosgene and bisphenol A, it has been found that unacceptable degradation begins to occur at temperatures on the order of 400°C. Therefore, thermally activated latently reactive moieties for use with polycarbonates based on phosgene and bisphenol A should preferably be activated at temperatures below 400°C. A preferred technique to provide a precursor component with a suitable latent, thermally reactive moiety is to utilize arylcyclobutene terminated carbonate polymers such as are shown in U.S. Patents 5, 198,527 and 5, 171 ,824. It has been found that the arylcyclobutene terminated carbonate polymers are readiiy processable at standard carbonate polymer processing conditions and can be very readiiy combined with and thoroughly dispersed in a second carbonate polymer component across a range of moiecular weights in the second component As shown, the arylcyclobutene moieties can then be heat or thermally activated to combine via the arylcyclobutene moieties to produce the stable, high molecular weight, branched polymer component These are especially preferred high molecular weight carbonate polymer components since the arylcyclobutene reaction does not require any free radical initiator or other activating compounds to initiate the addition reaction at reasonable temperatures and conditions for processing Bisphenol A-based polycarbonate Moreover, the arylcyclobutene reaction is exceptionally clean in that it does not simultaneously produce any low molecular weight byproduct materials as are typically resulting from many of the carbonate polymer crosslinking reactions The arylcyclobutene o combination reaction is relatively quick and sufficiently selective to produce a high molecular weight, branched carbonate polymer during an extrusion or molding process employing the precursor polymer In addition, it should be noted that substitution of the aryl ring of the arylcyclobutene compounds can be used to increase or decrease the reactivity of the cyclobutene group 5 In terms of the arylcyclobutene terminated caroonate polymers suited for use as the high molecular weight branched carbonate polymer component, it has been found desirable to incorporate the arylcyclobutene in amounts of at least 0 01 , preferably at least 0 02, and most preferably at least 0 03 mole arylcyclobutene moieties per mole diphenol monomer in the carbonate polymer to obtain suitable high molecular weight branched 0 carbonate polymer components Preferred arylcyclobutene terminated carbonate polymers suited for use as the high molecular weight branched carbonate polymer component would contain arylcyclobutene in amounts below that at which unacceptable levels of insoluble polymer gels are formed, desirably less than 0 5, preferably less than 0 4 and more preferably less than 0 3, and most preferably less than 0 2 mole arylcyclobutene moieties per mole 5 diphenol monomer in the carbonate polymer Other latent, thermally reactive moieties suitable for use in preparing high molecular weight branched carbonate polymer components include, for example, cyanate, biphenylene, vinyl, propargyl, acrylic, methacrylic and allyl It has been found that the desired combination of properties in the final blend 0 composition together is affected by the three way combination of the molecular weight, the level of branching, and the amount of the high molecular weight, brancned corrtDonent Therefore, these individual features deσend upon the others and can vary across fairly broad ranges In particular, the level of branching and the amount of the high moiecular weight branched component are closely related, with higher levels of branching reducing the amounts 5 of the component needed to provide a desired effect In the case of 'atently reactive moieties in the precursor component, the amount of latently reactive moieties in the HMWB PC Drecursor can be expressed as the number of moles of reactive moiety per mole oτ diphenol in the precursor PC component This is refe r red to as the mole per mole ratio or as "m/m " Then, the amount of latently reactive moieties in the mixture of the two PC components (pπorto reaction of those moieties) can be calculated as the m/m ratio multiplied by the weight percent of the latently reactive precursor PC component in the mixture ("wt percent"). In general, in the case of latently reactive moieties such as the arylcyclobutene moieties, it has been found that the latent reactive moiety concentration (which determines the amount of branching) and the amount of high molecular weight branched component should be selected such that the amount of latently reactive moieties in the mixture of the two PC components prior to their reaction (in units of m/m latent reactive moiety times wt percent precursor component) should be greater than 0 05, preferably greaterthan 0.1 , and most preferably greater than 0.15; and should be less than 2.0, preferably less than 1.75, and most preferably less than 1.50. It is otherwise difficult to directly measure the degree of branching in the branched, high molecular weight component, especially when this component has been prepared in situ by activation of a latently reactive moiety In general, however, it can be indirectly determined whetherthere is a sufficient degree of branching in the high molecular weight branched carbonate polymer by measuring the change in shear sensitivity due to the incorporation of the high molecular weight branched carbonate polymer in a carbonate polymer blend composition. It has been found that the high molecular weight branched component should have a degree of branching sufficient to provide an improvement or increase in the shear sensitivity of the resulting blend. In other words, the HMWB PC is sufficiently branched if it provides "shearthinning" in the final blend composition. This means that if the viscosities of the blend composition and the lower molecular weight carbonate polymer component alone are independently measured at increasing levels of shear, the measured viscosity of the claimed blend composition is observed to be reduced to a greater degree or at a greater rate than for the lower molecular weight carbonate polymer component without the high molecular weight branched component 't has been found that high molecular weight branched components with higher degrees of branching will provide shear sensitivity improvements at lower levels while lower degrees of branching will conversely require use of the component in larger amounts to provide shear sensitivity improvements These measurements of shear sensitivity can be done by standard techniques with dynamic mechanical spectroscopy (DMS). In particular, a fairly standard measurement techniαue for shear sensitivity of carbonate polymers involves measuring the complex viscosity of a polymer (η) under two different shear levels, 0.3 radians per second (lower shear) and 10 radians per second (higher shear) by dynamic mechanical spectroscopy at 280°C. Then, the ratio of those two numbers is determined, ηη(0.3/10) The value of the ηη ratio for the linear polycarbonate control sample is taken as a baseline value of 1. Values of the ηη ratio greater than 1.3, preferably greater than or equal to 1 .5, more preferably greater than or equal to 2, show that there is an "improvement" or "increase" m shear sensitivity as that term is used herein In general, the degree of branching can sometimes be directly determined in the high molecular weight branched carbonate polymer by measuring the concentration of reacted branching agent in an amount of the high molecular weight branched carbonate polymer prior to incorporation in the blend or that has been isolated from the carbonate polymer blend compositions according to the present invention The concentration of reacted branching agent in the high molecular weight branched carbonate polymer can typically be determined by IR or NMR spectroscopy or by liquid chromatography, depending upon the nature of the branching agent However, the lower levels of branching agent, although detectable by virtue of the shear sensitivity they impart, are very difficult to quantify by direct measurement techniques As mentioned above, the desired combination of properties in the final blend composition together with the level of branching in the high molecular weight, branched component determine the level of high molecular weight, branched component in the carbonate polymers According to the present invention a range of carbonate polymer blend compositions can be prepared to take advantage of the improved combinations of processability and improved properties obtainable in shaped articles In general, it has been found suitable to employ the first high molecular weight branched component in the carbonate polymer blend compositions in amounts of at least 0 1 weight percent, desirably at least 1 weight percent, preferably at least 2 weight percent and mo ** e preferably at least 3 weight percent, said weight percentages being based upon total amount of + he two carbonate polymer components in the blend compositions In order to maintain processability and thermal plasticity, the high molecular weight, branched component is employed in amounts less than or equal to 50 weight percent, preferably less than or equal to 35 weight percent, and more preferably less than or equal to 25 weight percent When using arylcyclobutene terminated carbonate polymers as the precursor component forthe high molecular weight branched carbonate polymer component, it has been found desiraσle to incorporate the arylcyclobutene-containing polymer in amounts sufficient to provide increased shear sensitivity in the resulting polymer It is generally desired to employ such polymer in amounts of at least 1 , preferably at least 2, more preferably at least 3 and most preferably at least 4 weight percent by weight arylcyclobutene-containing carbonate polymer in the preparation of composition according to the present invention In general it has been found that the advantageous property combinations can oe obtained using arylcyclobutene terminated carbonate polymers in amounts up to and including 40, preferably up to and including 30, more preferably up to and including 25, and most preferably up to and including 20 percent by weight based on the combined weight of the precursor and second carbonate polymer components The carbonate polymers suitable for use as the second, lower molecular weight carbonate polymer component are generally well known in the literature and a large numoe r are commercially available In general, these are preferably carbonate polymers prepared '-om one or more dihydnc components by reacting the dihydnc compound, such as a diphenol, with a carbonate precursor such as phosgene, a haloformate or a carbonate ester such as diphenyi or dimethyl carbonate Aromatic carbonate polymers are preferred and aromatic diphenols are preferred dihydnc compounds with the preferred diphenols including but not limited to 2,2- bιs(4-hydroxyphenyl)-propane (that is, bisphenol A); phenol, 4,4'-(9-H-fluorene-9-ylιdene)bιs (that is, bishydroxyphenylfluorene); 4,4'-thιodιphenol (TDP); 1,1-bιs (4--hydroxyphenyl)-1- phenyl ethane (bisphenol AP); phenolphthalein; bis (4-hydroxyphenyl) diphenyl methane, tetrabromobisphenol A (TBBA); and tetrachlorobisphenol A (TCBA) These lower molecular weight carbonate polymers can be prepared from such materials by any of several known processes such as the known interfacial, solution or melt processes As is well known, suitable chain terminators (typically monophenoiic compounds) can be employed to obtain the desired molecular weight in the lower molecular weight component. Optionally, branched carbonate polymers can be employed as the second, lower molecularweight carbonate polymer component These products are known and are prepared using the typical branching agents such as multihydπc compounds having three or more hydroxy groups, such as phenols having three or more hydroxy groups Generally, however, the linear carbonate polymers are preferred for use as the second, lower molecular weight component where the improvement in shear sensitivity is more noticeable with addition of the high molecular weight branched component The carbonate polymers suitable for use as the second, lower molecular weight carbonate polymer component in the present invention also include carbonate polymers prepared from two or more different multihydroxy compounds, preferably dihydroxy compounds, and preferably phenols, or a combination of a multihydroxy compound, such as a diphenol, and a glycol or a hydroxy- or acid-terminated polyester or a dicarboxyi c acid n the event a carbonate copolymer or heteropolymer is desired It is also possible to employ multifunctional carboxylic acids or derivatives, especially aromatic carboxylic acds including their acid chlorides, and prepare poly(ester-carbonate) resins such as the known aromatic poly(ester-carbonates) The known silicon-containing multihydπc monomers can also be used to prepare silicon-containing carbonate polymers that are suitable for use in the blends according to the present invention Also suitable for use as the second, lower molecular weight carbonate polymer components for practice of the invention are blends of two or more of the above-described lower molecular weight carbonate polymer comoonents. For purposes of obtaining desired property combinations, it has been found that the second, lower molecular weight carbonate polymer component should have a weight average molecular weight of at least 10,000, preferably at least 13,000, more preferably at least 15,000 ano most preferably at least 17,000 n order to keep the desired level of polymer me t flow and processability it has been found tnat the second, lower molecular weight carbonate polymer component should preferably have a weight average molecular weight of no more than 60,000, preferably no more than 55,000, more preferably no more than 50,000, most preferably no more than 40,000. It is understood that the second, lower molecular weight components suitable for use according to the present invention may be a single component carbonate polymer directly obtained from a polymerization process. On the other hand, commercially available carbonate polymers which will be suitable for use as the second, lower molecular weight component are often actually a combination of two or more different carbonate polymer components of differing molecular weights and melt flow rates. It is obviously necessary for carbonate polymer suppliers to provide the broad range of potential customers and applications with an equally broad range of different carbonate polymer products that vary in their balance of processability (that is, melt flow rate) and performance properties. However, a polymerization facility can produce only a limited number of different polymers, typically near the higher and lower molecular weight extremes. These polymers are then blended to obtain the desired intermediate melt flow rate product. These types of products, will then have an average molecular weight which would then be determinative of their suitability for use as the lower molecular weight second carbonate polymer component in the blend compositions according to the present invention. It is also known that "branched polymers" such as the HMWB carbonate polymers used in the blends according to the present invention comprise only a portion of polymer molecules that are actually branched, the balance being essentially linear. However, as used herein, the term branched carbonate polymer refers to the entire polymer component and not just to the fraction of the molecules of that component that are actually branched. In preparing the blend compositions according to the invention it is important to employ mixing techniques that result in sufficient mixing of the two components, preferably obtaining a thorough, generally homogeneous mixing of the two components. Suitable processes are generally known to those skilled in this area, examples of techniques that can be used to homogeneously mix the first or precursor component with the second component include solution blending and melt blending in known melt mixing equipment such as single or twin screw extruders, molding equipment, Banbury mixers or the like. A further aspect of the invention, as mentioned above, is an improved process for preparing the disclosed carbonate polymer blends comprising the steps of (a) preparing a precursor component capable of forming the first high molecular weight branched carbonate polymer component, said precursor component comprising a carbonate polymer containing latent thermal ly artivated reactive moieties; (b) combining the precursor component with the second carbonate polymer; and (c) thermally activating the latently reactive moieties of the precursor component during or after their combination to provide a generally homogeneous carbonate polymer blend composition. The combination of the precursor and second components can be done by solution blending using known solvents and techniques The first component precursor can also be combined with the second carbonate polymer by dry blending or dual feeding the precursor and second components. As known, dry blending involves combining and mixing the polymer in the form of powder, pellets, flakes or similar unmelted form. Dual feeding is performed using a K-tron brand feeder, a screw feeder, a weigh belt feeder or the like to separately convey the resins in an unmelted form to the inlet(s) or feed port(s) of a melt mixing device. Then, the dry mixture or dual feeds are supplied to an extruder or other melt mixing device. As noted, the combining step (b) can be done at a temperature and/or for a time o sufficient for the latently thermally reactive moieties to become significantly activated and reacted to form the HMWB PC component, providing the blend composition which can be used in appropriate applications. Another process aspect involves combining the precursor component in step (b) with the second carbonate polymer component at a temperature and for a time less than 5 sufficient to significantly thermally activate the latently thermally reactive moieties and (3) recovering an intermediate carbonate polymer blend composition. The intermediate resin blend would then contain both the the precursor component and the second carbonate polymer component. The intermediate could be further processed and/or shaped prior to, during or subsequent to the thermal activation of the latent reactive moieties. Another process 0 aspect involves thermal activation of the latently reactive moieties of the precursor component in an extrusion or molding step to directly provide a shaped article prepared from the claimed carbonate polymer blend composition. In this way, this preferred process provides an intermediate carbonate polymer blend composition comprising a carbonate polymer precursor component having one or more 5 latently reactive moieties which component is capable of forming a high molecular weight branched carbonate polymer upon heat activation and a second, different carbonate polymer component having a lower molecular weight than the high molecular weight branched component. A further preferred embodiment involves incorporating latently thermal reactive moieties in the first carbonate polymer component precursor in an interfacial polymerization 0 process. In addition, when using a carbonate polymer precursor component that has latent reactive moieties and premixing the precursor with the second polymer component, it is important to perform the mixing under appropriate conditions to assure that there is good mixing of the polymers as the polymers melt. In particular, it is desirable if the molecular 5 weights, and physical forms and sizes (that is, pellets, flake, powder, etc.) of the polymers are selected to be within respective ranges so that both components begin to melt at about the same point in the melt mixing process. In this way, the precursor polymer will then be more homogeneously mixed to form a better intermediate. Otherwise, if preparing the high molecularweight branched component directly, the precursor polymer will then be more homogeneously mixed and dispersed by the time the thermally activated latent reactive moieties began to inter-react. For example, if attempting to mix a powder form of precursor polymer with a pellet form of the second polymer component, the powder form precursor polymer may tend to melt more quickly and might begin inter-reaction prior to thorough melt mixing with the second component. Unless the process temperature is maintained sufficiently low, this may lead to undesirably large gels or domains of high molecular weight or crosslinked polymer. This can be prevented by using a second component which is similarly in powder form and/or has a lower molecular weight and/or lower glass transition temperature (Tg). The blend compositions according to the present invention are particularly well suited for applications that take advantage of the surprisingly good combinations of shear sensitivity, processability and melt strength. The blend compositions according to the invention exhibit a relatively high melt strength or high melt viscosity at low shear conditions and are unexpectedly easily processed at standard shear rates generated by typical melt processing equipment. This means that they are especially well suited for applications such as fiber forming, blow molding, thermoforming or profile sheet production where reasonably high melt strength is needed. In a related aspect, the present invention is also an improved process for preparing a fiber com prising the step of forming a fiber from a blend as described above, comprising the high molecular weight branched carbonate polymer component. Fiber forming process that can be applied to carbonate polymers are generally known to those skilled in the art and the use of the high melt strength carbonate polymer compositions according to the present invention provides an improvement in terms of melt strength, reduced necking and maintaining fiber diameter in very thin fibers. As also known to those skilled m the art, the term 'fiber" when used in connection with carbonate polymers refers to strands that have a diameter of from 0.1 to 1.5 millimeter and a length of at least 2 millimeters A further aspect of the blend compositions according to the present invention is the surprisingly good drip resistance under flame testing conditions, leading to the improved ignition resistance properties of these blends. One of the criteria in ignition resistance testing is resistance to the tendency to generate flaming drips of molten polymer under test conditions. In actual fire situations the molded plastic part is then believed to be less likely to spread a fire to other fuel sources. Polytetrafiuoroethylene antidπp additives (Teflon) are known but their incorporation into carbonate polymers requires additional, complicated processing steps and has a detrimental effect on other polymer properties, particularly impact resistance and transparency. The polymer compositions according to the invention are surprisingly resistant to the dripping characteristic and can be advantageously used where ignition resistance properties are desired. Optionally, transparent, ignition resistant, carbonate polymer blend compositions can be obtained using a high molecular weight branched carbonate polymer drip reducing additive together with a second different carbonate polymer having a lower molecular weight than the high molecular weight branched component. It should be noted that other optional ignition resistance additives must be properly selected to maintain the desired levels of Iight transmission and haze if transparency is intended. These blends can be used to prepare improved shaped articles having good combinations of Iight transmission (transparency or translucency) and ignition resistance. Preferably, blends and articles can be prepared according to the invention wherein the ignition resistance of the blend, when tested according to UL 94 is rated at least V-0 at 1/8 inch (3.175 mm) or is more ignition resistant (for example, rated 5- at 1/8 inch). In a another embodiment, the high molecular weight branched carbonate polymer drip reducing additive is formed under ignition conditions from a precursor component capable of forming a high molecular weight branched carbonate polymer upon heat activation. As mentioned, additional ignition resistance additives can be employed at appropriate levels where the desired levels of Iight transmission and low color are maintained. Such additives can include halogenated carbonate polymers and oligomers, such as brominated polycarbonates and oligocarbonates and inorganic and organic salts or alkali and alkali earth metals. A further aspect of the blends according to the present invention is that the high molecular weight branched component can be employed to provide Iight diffusing and gloss controlling effects, if such effects are desired and if appropriate processing conditions are employed. Many applications for opaque carbonate polymers, such as automotive parts, desire a controlled gloss or matte finish on the surface of the molded part. Other applications desire varying degrees of Iight transmission together with Iight diffusing effects. Such applications include frosted, mottled, semi-transparent or translucent parts like f luorescent lighting diffusers, shower doors and non-glare glazing for picture frames It has surprisingly been found that the blends according to the present invention can produce such Iight diffusing or controlled gloss effects and maintain sufficient levels of Iight transmission. The amount of gloss reduction/light diffusion has been found to be a function of the amount of the high molecularweight branched component, particularly when a latent reactive arylcyclobutene moiety is being used to provide the branching. It has also been found that the use of high shear melt processing of the blend into molded parts, such as when injection molding, will provide the greatest reductions in the gloss and/or Iight diffusing effects in the parts. When a latent reactive arylcyclobutene moiety is being used to provide the branching, high shear melt processing of the blend into molded parts at or above temperatures required for thermal activation of the arylcyclobutene moiety provide the greatest reductions in the gloss and/or Iight diffusing effects in the parts. This reduces the need for special surface treatment of the molds or for subsequent surface treatment steps for the molded articles As used herein, the term "reduced gloss" means that the incorporation of the high molecularweight branched component results in a molded article having lower gloss than an article molded under the same conditions from the same composition not containing the high molecularweight branched component In general, "low gloss" polymer or resin, as used herein, refers to a polymer or resin, when molded into plaques and tested for gloss according toASTM D-523-85 exhibits 60° gloss values of less than 70 percent, preferably less than 60 percent As used herein the term "transparent" means that molded articles have a measured total light transmission value according to ASTM D-1003 of at least 40 percent, more preferably at least 60 percent, more preferably at least 80 percent and a diffused light transmission value of less 7 percent, preferably less than 5 percent As used herein the terms "semi-transparent", "frosted", "mottled" and "translucent" are generally synonymous and mean that molded articles have a measured diffused light transmission value according to ASTM D-1003 of at least 7 percent, more preferably at least 15 percent and most preferably at least 20 percent and would have a total light transmission value of at least 40 percent, more preferably at least 50 percent and most preferably at least 60 percent Previously, in order to obtain light diffusion/reduced gloss effects in articles prepared from carbonate polymers that were transparent, semi-transparent or translucent it had been necessary to use additional process features or incorporate additives which had a detrimental effect For example, when using a mold with roughened or embossed surface to provide such effects, the surface of the mold tends to wear out unevenly with time Incorporating gloss reducing fillers normally causes the material to lose impact and light transmission properties The present invention provides a composition and process that do not have these disadvantages and can produce these effects in shaped articles prepared by extrusion, blow molding, thermoforming or injection molding techniques with a smooth surface mold and without a subseαuent gloss reducing surface treatment Obviously further surface modifications can also be obtained using known surface treatments In a further embodiment of the present invention, the controlled gloss, transparent, semi-transparent or translucent articles could also be obtained using another additive having sub-micrometer size particles at low levels such that the desired physical properties are not detrimentally affected while the desired light transmission and controlled gloss are obtained A further aspect of the present invention is the ability to employ recycle, regπnd, contaminated and/or scrap carbonate polymer as all or part of the second, carbonate polymer component and effectively upgrade those types of materials with the high molecular weight branched component As known by the producers and users of thermoplastic carbonate polymers, the typical processes for preparing these polymers or resins and for preparing molded, extruded or otherwise shaped articles tend to produce varying amounts of recycle, regrind, contaminated and/or scrap carbonate polymer As used herein, this refers to polymer or resin which has undergone a change or loss in the physical, rheological or optical properties versus the optimized properties typically possessed by the resin when it is initially extruded and pelletized. This degradation can be brought about by a number of conditions such as prolonged air exposure of the high temperature melt and repeated melt plastifications As known, these conditions, particularly in the presence of contaminants or impurities such as pigments, paints, coatings and additives, can degrade the polymer molecular weight and cause change or loss of physical, rheological or optical properties. Typically, the recycle, regrind, contaminated and/or scrap carbonate polymer has been rejected for one or more of these reasons. The incorporation of the high molecular weight branched component, particularly by incorporation of a precursor component, either at the extruder or molding machine, can restore these properties and/or upgrade the resin to make it suitable for use in the same or different shaping processes In general, it has been found that all or part of the second carbonate polymer in the compositions according to the present invention can be a recycle, regrind, contaminated and/or scrap carbonate polymer. In particular, the second carbonate polymer in the blends according to the present invention can employ at least 5, preferably at least 10 and more preferably at least 30 weight percent recycle, regrind, contaminated and/or scrap carbonate polymer. In addition to the high and lower molecular weight components, and provided that the desired property combinations are maintained to a satisfactory degree, the carbonate polymer compositions according to the present invention can advantageously contain the standard types and amounts of the additive-type components frequently incorporated into carbonate polymers. These components can include ignition resistance additives, fillers (that is, glass fibers, talc, clay, etc.), pigments, dyes, antioxidants, heat stabilizers, ultraviolet Iight absorbers, mold release agents, impact modifiers, antistatic additives, flow aids, lubricants, additive for reducing melt fracture and the other additives commonly employed in carbonate polymer compositions. Experiments The following Experiments are given to further illustrate the invention and should not be construed as limiting its scope In the following Experiments, all parts and percentages are by weight unless otherwise indicated Preparation of a Benzocyclobutene-terminated Polycarbonate ("BCB PC") Benzocyclobutene-terminated polycarbonates ("BCB PC"), precursor components having latently reactive arylcyclobutene moieties capable of forming a high molecular weight branched carbonate polymer upon heat activation, were initially produced by the following interfacial process. A glass reactor was fitted with a mechanical stirrer, a baffle, a thermometer, a pH electrode connected to a oH meter/controller, a liquid inlet tube, a gas inlet tube and a gas outlet tube connected to a phosgene scrubber, the scrubber containing an aqueous solution of 50 weight percent sodium hydroxide and about 1 percent by weight tnethyiamine To the reactor was added 68 5 weight parts (0 3 mole parts) bisphenol A, 2 16 weight parts (0 018 mole parts) 4-hydroxybenzocyclobutene (BCB-OH), 360 weight parts water and about 240 weight parts dichloromethane While stirring the reaction mixture there were added 48 weight parts (0 6 mole parts) of sodium hydroxide in a 50 weight percent aqueous solution followed by the addition of 37 weight parts (0 375 mole parts) of gaseous phosgene at a rate of about 1 weight part per minute The sodium hydroxide addition was maintained as needed to maintain a pH of about 12 5 Following the phosgene addition, 515 weight parts dichloromethane and 0 3 weight parts (1 mole percent) tnethyiamine were added The reaction mixture was agitated for 20 minutes to produce a bisphenol A polycarbonate resin terminated with benzocyclobutene moieties The pH of the mixture was reduced to about 7 by the addition of 9 weight parts of phosgene The polymer solution was washed with 1 N HCI and with water and the polymer was then isolated The polymer molecular weight was determined by gel permeation chromatographic (GPC) analysis, the weight average molecular weight (Mw) being 18,190 Liquid chromatographic analysis of the reaction mixture residue showed complete reaction of the 4-hydroxybenzocyclobutene The resulting polycarbonate, oefore any crosslinking, was therefore determined to contain 0 06 moles benzocyclobutene per mole bisphenol A and have a degree of polymerization of about 27 The terminal location of the benzocyclobutene moieties was determined by reverse phase liquid chromatography using the conditions described by D J Brunelle et al , "Remarkable Selective Formation of Macrocyclic Aromatic Carbonates Versatile New Intermediates for the Synthesis of Aromatic Polycarbonates", J of Am Chem Soc (1990) vol 1 12, p 2399 A bonded silica column using tetrahydrofuran/water gradient was employed to separate oligomer components Their retention times and UV soectra were compared to determine the types of oligomer end groups Using the process as described above and adjusting the amounts of aqueous sodium hydroxide, water, phosgene and methylene chloride, two additional arylcyclobutene terminated aromatic carbonate polymers were prepared having the molecular weights and arylcyclobutene concentrations as shown in Table I 'n Table I the ratio of the moles hydroxybenzocyclobutene to the moles of bisphenol A in the polymer is shown as "Mole Ratio " As shown in Table I, varying the amounts of BCB-OH results in the indicated range of polymer compositions and molecular weights The table shows molecular weight (Mw) of the resulting BCB PC which is the precursor to the high molecular weight branched carbonate polymer (HMWB PC) as well as the moiecular weight of the HMWB PC component that resulted from reaction of that BCB PC The Mw of the resulting HMWB PC was determined by GPC analysis of the molecular weight distribution of blend compositions after the BCB PC had been fully reacted to form the HMWB PC. For the purposes of these tests, 20 weight percent of the 0.03 m/m BCB PC was blended with 80 weight percent of a 20 MFR linear PC, while 7 and 3.5 weight percentages of the 0.06 and 0.1 m/m BCB PC's, respectively, were blended with the balance of a 13 MFR PC resin. Then, the latently reactive BCB moieties of the precursor component were thermally activated to provide a homogeneous carbonate polymer blend composition containing the HMWB PC. The blend was analyzed by GPC and the high molecular weight portion of the molecular weight distribution curve was mathematically analyzed to determine the Mw of the HMWB PC component. Table I - High Molecular Weight Branched Polycarbonates ("HMWB PC") Branching Agent Mw No. Before Reaction After Reaction Type (Mole Ratio) (Precursor) (HMWB PC) A BCB 0.03 31,894 99,100 B BCB 0.06 18,190 676,500 C BCB 0.1 11,634 234,000 These or similar BCB PC polymers were used to prepare the HMWB PC components in the blends prepared below. Table II below summarizes the series of second, lower molecular weight polycarbonate resins that are used in preparing the example and comparison blend compositions. Table II - Lower Molecular Weight Polycarbonates No. Type Mw MFR I Linear 36,000 3.5 II Linear 32,000 6 III Linear 26,500 13 IV Linear 24,000 20 V Linear 19,000 60 VI Linear 18,000 80 VII Branched 36,000 2.5 The blend compositions that are shown in the following tables we r e prepared as indicated The HMWB PC component precursors based on the BCB PC used in these and subsequent experimental compositions was observed to have blended homogeneously with the second component Also, in the final products, the HMWB PC components based on the BCB PC were observed to form homogeneous blends with no visually observable phase separated components in the resulting blend compositions Analysis of the mixtures for insoluble crosslinked polycarbonate gave 3 percent or less by weight For all of the blends shown in the tables, the Tg was about 150°C Then, as shown, parts were successfully molded from the blend compositions and were tested according to the indicated methods with the o results reported below For measurement of the "Melt Strength" the following test was used, as described in U S Patent 5,094,806 ASTM Type I tensile bars (see ASTM designation D 638-87b) are prepared by injection molding on a 70 ton Arburg molding machine Mold temperatures in the range of 150 o F-175°F (65 to 80°C), are used in molding the tensile bars from the various 5 compositions Various amounts of weight are attached to one of the ends of each of the predπed tensile bars and the bars are hung vertically in a forced air oven for 5 minutes at a ■ emperature of about 200°C or 175°C (as indicated in the respective table), which is about comparable to the melt temperature at which these compositions would be blow molded The weight reported as the "melt strength" or "Equil Load (Grams)" for each sample is the amount 0 of weight which could be attached to the bar before it showed any detectable elongation under these conditions at the selected temperature The dramatic increase in the amount of weight which a tensile bar can support without elongation at elevated temperatures, resulting from the presence of a high molecular weight branched polymer component, can be clearly seen from the following data 5 As used herein the term "DTUL" is the deflection temperature under a load of 264 psi as measured according to ASTM D 648-82 Flexural modulus is measured according to ASTM D 790-84a and the tensile strength and the elongation are measured according to ASTM D 638- 84 Where reported, the notched Izod impact strength is measured on a test bar sample having dimensions of 1/2 inch by 2 1/2 inches (12 7 mm by 63 5 mm) and having a notch of 10 mil 0 (0 0254 mm) according to ASTM D 256-84 The melt flow rate (MFR) values are measured according to ASTM D 1238-85, conditions of 300°C and 1 2 kilograms mass and are reported in grams per 10 minutes (gr/10 mm) Melt Strength of Blend Compositions Blend compositions were prepared as indicated in Table III below containing a 5 lower Mw base PC resin in powdered form and a BCB PC component (in flake form) to provide the HMWB PC The indicated components were dry blended, then melt mixed on a 1 1/2 inch (38 mm) single screw Killion extruder at a temperature of about 430° ρ (220°C) and pelletized At this point the BCB moieties were not yet significantly reacted and the HMWB PC was not yet formed. The intermediate blend composition obtained can be further processed, by injection molding, for example, into shaped articles. The HMWB PC component can then be obtained prior, during or subsequent to the processing into the desired shaped article. For the melt strength test samples, the BCB PC was then reacted to form the HMWB PC during the injection molding step when the blend composition was injection molded into test bars at a temperature of about 305°C. TABLE III - Blend Composition Melt Strength HMWB PC Lower Mw Base PC Product (BCB-TYPE) Melt Blend Strength Comp. No. Equil. Load Wt% Mole e PC itirie (Grams) % BCB Mw** t% Typ MFR Mw at 20TPC 1* 0 - - 100 Lin 13 26,500 2 2* 0 - - 100 Lin 3.5 36,000 12 3* 0 - - 100 Br 2.5 36,000 36 4 5 0.06 18,000 95 Lin 13 26,500 56 5 7 0.06 18,000 93 Lin 13 26,500 116 6 9 0.06 18,000 91 Lin 13 26,500 200 7 3.5 0.1 11,000 96.5 Lin 13 26,500 50 8 5 0.1 11,000 95 Lin 13 26,500 76 * Not an example of the present invention **As measured before reaction *** Lin=linear, Br=branched As can be seen, the blend compositions according to the invention have improved melt strength properties over the linear PC base resin and over a branched PC resin not containing a high molecular weight branched carbonate polymer component. Ignition Resistance of Blend Compositions A blend composition was prepared comprising 5 percent by weight of a first, high molecular weight branched component based on flake BCB PC (0.1 m/m BCB, 10,000 mol wt) and 95 percent by weight of a second, lower molecular weight polycarbonate component of powdered polycarbonate having a molecularweight of 26,500 These components were initially dry blended as powders and extruded at 280 c C on a 30 millimeter Werner and Pfleiderer (WP) twin screw extruder and pelletized. At this point the BCB PC was found by liquid chromatographic analysis to be partially reacted, forming a portion of the high moiecular weight branched component by the heat treatment To this blend composition were added the following ignition resistance additives (0.1 percent by weight potassium N-(p-tolylsulfonyl)-p-toluene sulfimide (KPTSM), 0 1 percent by weight hydrogen N-(p-tolylsulfonyl)-p-toluene sulfimide (HPT5M) 1.0 percent by weight BC- 52 brand brominated oligocarbonate. The additives were incorporated by blending and extruding at 31 1°C on a 30 mm WP twin screw extruder. At this point the BCB PC was found to be fully reacted to have formed the high molecular weight branched component by the heat treatment. This composition was molded into test bar samples at 340°C on a 70 ton Arburg molding machine at a mold temperature of 180°F (82°C). The HMWB PC component was observed to have blended homogeneously with the second component. These samples were then evaluated and the following properties were observed: Table IV - Ignition Resistant Composition Properties This composition is an improvement over compositions which utilize Teflon as an antidrip agent to obtain V-0 rating since the use of Teflon produces an opaque blend and results in a loss of impact properties. Controlled Gloss Compositions The compositions shown in Table V were prepared by dry blending the indicated powdered linear PC and flake BCB PC components and melt mixing on a 30 mm co-rotating twin screw WP extruder at 230°C and recovering the pelletized intermediates with the HMWB PC not believed to be significantly formed. Test plaques were then molded on a 70 ton Arburg injection molding machine at 320°C with a mold temperature of 150°F. This process provided moderate to high shearing during the melt extrusion and flow into the mold The gloss measurements are performed according to ASTM D-523-85 using a Dr. Lange Reflectometer RB3 model test apparatus from Hunter Associates Table V - Controlled Gloss Properties Comparison Composition No. 9* 10 PC (21.000 mol wt, 2000 gm 1800 gm linear) BCB-PC (18,000 mol wt)** 0 200 gm Carbon black 4 gm 4 gm Properties 20° gloss 85 6 60° gloss 101 20 85° gloss 99 53 Izod (10 mil Notched) 2.5 ft/lbs 10 ft/lbs (132 J/m) (535 J/m) *Not a sample of the present invention **Prior to reaction; 0.06 Mole/Mole BCB As can be seen, the added HMWB PC provided excellent gloss reduction while actually improving the product toughness Translucent Compositions The following compositions were prepared and tested for translucence. In preparing the Blend No. 1 1 formulation, 72.2 weight percent of the 18,000 Mw linear PC pellets and 27.8 weight percent of powdered 26,500 Mw linear PC were dry mixed, extruded on a Werner and Pfleiderer 30 mm co-rotating twin-screw extruder at 230°C and pelletized. In preparing the Blend No 14 formulation, 65 weight percent of the 18,000 Mw PC pellets, 25 weight percent of powdered 26,500 Mw linear PC and 10 weight percent of the 18,000 Mw (0 06 m/m) BCB-PC flake were mixed in the same fashion as was used to prepare Composition 1 1 In preparing blend formulations numbered 12 and 13 in the following Table VI, 75 and 50 weight percent, respectively, of the 18000 Mw linear PC were combined with a premix of 25 and 50 weight percent respectively of Blend No 14 by dry blending at the molding machine Blend No 15 was prepared in the same fashion as Blend 1 1 using 90 weight percent of the 21 ,600 Mw branched PC pellets and 10 weight percent of the 18,000 Mw (0 06 m/m) BCB-PC flake For the Blend No 16 formulation, 60 weight percent of the 18000 Mw linear PC pellets, 20 weight percent of powdered 26,500 Mw linear PC and 20 weight percent of the 18,000 Mw (0.06 m/m) BCB-PC flake were blended using the same process as used with Blend 1 1 The compositions were dried at 120°C for 4 hours prior to molding on a 70 ton Arburg molding machine set at 305°C A smooth surfaced ASTM mold set at 175°F (80 C C) was used to mold 2 5 inch (63 5 mm) disks, tensile bars and DTUL bars which were evaluated as removed from the mold without any subsequent gloss reducing surface treatment The following measurements were made on a Color Quest instrument from Hunter Associates Laboratory according to ASTM D-1003 As used in Table VI, these terms have the indicated meanings: Diffuse Transmission: Process by which incident light, while being transmitted through an object, is redirected or scattered over a range of angles Regular Transmittance * Process by which incident light is transmitted through an object in a linear, straight tnrough manner, without diffusion Total Transmission Diffuse Transmission + Regular Transmission % Haze = % Diffuse Transmission x 100 % Total Transmission Table VI - Translucent Properties HMWB Lower Mw Base PC Transmittance Properties PC UL -94 Blend (BCB PC) No. (1/8 Total Diffused Haze inch) Wt% Wt % Type Mw (%) (%) (%) 11 * 0 72.2 Lin 18 ,000 89.9 0.8 0.9 Fail 27.8 Lin 26 ,500 12 2.5 91.25 Lin 18 ,000 86.9 27.9 31 .9 V-2 6.25 Lin 26 ,500 13 5 82.5 Lin 18 ,000 88.3 40.3 45.4 V-0 12.5 Lin 26 ,500 14 10 65 Lin 18 , 000 86.5 55.0 63.6 V-0 25 Lin 26 ,500 15 10 90 Br 21 , 600 86.7 54.1 62.3 V-0 16 20 60 Lin 18 ,000 77.3 58.2 75.2 Fail 20 Lin 26 ,500 *No a n exam Die of the prese nt mventioi 1. As can be seen, the HMWB PC component results in large increases in the light diffusing properties of these compositions. Surprisingly, there is additionally a simultaneous improvement in ignition resistance for most of the compositions In comparing the effects of a HMWB PC to a lower molecular weight branched PC with regard to Iight diffusing ability and melt strength, various compositions were evaluated as shown in Table VII. For Composition No 18*, 95 weight percent of the 18,000 Mw linear PC pellets and 5 weight percent of 36,500 Mw branched PC were dry mixed and extruded on a Werner and Pfleiderer 30 mm co-rotating twin-screw extruder at 235°C and pelletized 'n preparing Composition No. 19*, 90 weight percent of the 18,000 Mw linear PC and 10 weight percent of 36,500 Mw branched PC were dry mixed and extrudeσ on a Werner and Pfleiderer 30 mm co-rotating twin-screw extruder at 240°C and pelletized. In preparing Composition No. 20, 95 weight percent of the 18000 Mw linear PC and 5 weight percent of 18,000 Mw BCB-PC flake were dry mixed and extruded on a Werner and Pfleiderer 30 mm co-rotating twin-screw extruder at 230°C and pe'letized. In preparing Composition No 21 , 90 weight percent of 18000 Mw linear PC pellets ana 10 weight percent of 18,000 Mw BCB-PC flake were combined according to same process as used or Composition No 20 The compositions were all dried at 120°C for four hours pπor to molding on a 70 ton Arburg molding machine at 310°C A smooth ASTM mold set at 175°F (80°C) was used to mold 2 5 (63 5 mm)ιnch disks, tensile bars and DTUL bars The light transmission tests were the same as performed forthe preceding Table VI compositions The melt strength tests were the same as performed above for the Table III compositions but at 175°C, a slightly lower temperature Table VII Higher versus Lower Mw Branched PC Melt Branched PC Light Transmission Properties Strength Comp. Equil. No. Load (Grams) Wt% Type Total (%) Diffuse (%) Haze (%) at 175°C) 17* 0 88.5 0.4 0.4 0 18* 5 Low Mw 89.7 0.6 0.5 1 19* 10 Low Mw 90.5 1.0 1.1 5 20 5 High Mw 89.1 7.3 8.2 60 21 10 High Mw 86.4 49.9 57.8 >635 Not an example of the present invention. As can be seen, the HMWB PC provides much larger benefits than lower molecular weight branched PC with regard to both light diffusing properties and melt strength Blend Composition Thermal Stability Evaluation Heat testing a blend of a HMWB PC (based on BCB PC) with a lower molecular weight polycarbonate shows that the BCB PC based materials provide HMWB PC components with excellent thermal stability as shown in Table VIII below These tests were conducted on polymer films prepared from dichloromethane solutions of a blend comprising 20 wt percent 0 06 m/m BCB PC and 80 wt percent of an 80 MFR linear PC The blends were prepared by solution blending the components in the dichloromethane at room temperature with the HMWB PC being formed by the reaction of the BCB during a 6 minute heating period up to 300°C The blends all had Tg values of about 150°C The film samples of the alloys and PC controls were exposed to heating at 300°C under nitrogen forthe indicated times and analyzed by GPC for molecular weight (Mw or weight average, Mn or number average, and Mz or "z" average), by UV spectrophotometry for total absorbance at 288 nm ("Abs. 288 nm"), and visually for color (see Table VIM) Heating the control PC for 40 mm. at 300°C produced no significant change in molecular weight or coior The BCB PC'PC olend showed a rapid increase in molecular weignt as the BCB PC fraction reacts to form the HMWB PC, after which the polymer molecular weight does not significantly change (less than 5 percent change in Mw). The color of the BCB PC/PC alloy remains low throughout the test, becoming slightly yellow, but not dark or brown in color. It can therefore be seen that these HMWB PC components and the resulting blend compositions according to the invention are thermally stable at a temperature 100°C above the Tg of the carbonate polymer blend composition, which was about 150°C in this case. Effects of Various Molecular Weights and Branching Degrees in the HMWB PC The compositions shown in Table IX were prepared by solution mixing of the indicated BCB PC with a 22 MFR linear PC in dichloromethane at room temperature followed by precipitation with hot water (90 to 100°C) followed by compression molding starting at 200°C and heating to 300°C. The BCB PC was reacted to form the HMWB PC during this molding. The HMWB PC components were prepared from the indicated BCB PC's (from Table I). As can be seen in Table IX below, the higher concentrations of the HMWB PC component (the greater degrees of branching) significantly increase the low shear viscosity (decrease the melt flow rate) of the compositions prepared. Table IX. Effect of HMWB PC Molecular Weight on Blend MFR ( 22 MFR PC ) M „ ™ « - HPT * Wt . % BCB Wt . %BCB PC % BCB Total MT7D No. m/m BCB in BCB PC in BIend ( m /m x wt% ) ^ 24* - - 0 - 22 25 0 0..0033 1 1..4400 6.00 0.08 22.5 26 0 0..0033 1 1..4400 14.00 0.20 13.4 27 0 0..0033 1 1..4400 20.00 0.28 8. 1 28 0 0..0066 2 2..7755 3.00 0.08 21 .6 29 00..0066 22..7755 7.00 0. 19 6. 1 30 00..0066 22..7755 10.00 0.28 2. 7 31 00.. 11 44..5511 1 .50 0.07 24.5 32 00.. 11 44..5511 3.00 0. 14 4.4 33 00.. 11 44..5511 7.00 0.32 >0.5 34 00..11 44..5511 10.00 0.45 >0.5 * Not an example of the present invention. In Table X it is is shown that blends based on HMWB PC improved in melt strength (Equil. Load) as shown by the increased loads that can be supported and Shear Sensitivity (processability) as shown by the lower η/ηratio while they maintained their toughness The blends of Table X were prepared by the process described above and used for preparing the blends of Table III. The shear sensitivity measurements for the polymers of Tables X and XI were done by dynamic mechanical spectroscopy (DMS), as mentioned above The viscosity (η) of the polymer was measured under two different shear levels, 0.3 radians per second (lower shear) and 10 radians per second (higher shear) by dynamic mechanical spectroscopy at 280°C Then, the ratio of those two numbers is determined, ηη(0.3/10). The value of the ηη ratio for the linear polycarbonate control sample was then taken as a baseline value of 1. The ηη ratios for the other sample were converted to comparable values by dividing by the value of the ηη ratio for the linear polycarbonate control sample. Values of these ηη ratios greater than 1 , preferably greater than or equal to 1.5, more preferably greater than or equal to 2, snow that there is an "improvement" or "increase" in shear sensitivity as that term is used herein The values for shear sensitivity, ηη(0.3/10), are a unitless ratio of the viscosity measurements as determined by dynamic mechanical spectroscopy at 280°C. Table X. Effect of HMWB PC Concentration on Rheological and Impact Properties HMWB PC Base PC Blend Properties No. Wt. Wt.% Wt. % Equil. Shear Izod % in m/m Wt% BCB in Load at sensitivity Impact MFR MFR Blend BCB BCB in Blend 200 °C η/η ft. Ib./in. Blend ia . (0.3/10) (J/m) 35* - - - - 100 13.0 13 2 1.00 17 (900) 36 5.0 0.06 2.75 0.14 95 13.0 4.4 56 1.56 16 (850) 37 7.0 0.06 2.75 0.19 93 13.0 1.5 116 1.92 15 (800) 38 9.0 0.06 2.75 0.25 91 13.0 1.1 200 2.22 16 (850) *Not an example of the present invention. The samples shown in Table XI were prepared by solution blending the components in dichloromethane precipitation in hot water. In Table XI it is is shown that blends based on 200,000 Mw linear PC were not significantly improved in processability as shown by the lower η/ηratio (improved shear sensitivity). In Table XI, the high molecular weight PC is linear and has an Mw of 200, 000 and the MFR was not measurable. Table XI . Effect of High Molecular Weight PC on PC Shear Sensitivity No . Base PC High Molecular Weight PC Shear sensitivit Wt . % Mw MFR Wt . % Mw n /η ( 0.3/ l 55 39* 100 26 ,500 13 0 200 ,000 1 40* 95 26 ,500 13 5 200 ,000 1 . 20 41* 91 26 , 500 13 9 200 ,000 1 .27 >Not an example of the present invention. As understood by those skiiled in this art, there are many other embodiments of the invention in addition to these represented above. These examples, therefore, cannot be construed as limiting the scope of this invention in any way.

Claims: CLAIMS: 1. A carbonate polymer blend composition comprising a first high molecular weight branched carbonate polymer component and a second, different carbonate polymer component having a lower molecular weight than the first component, characterized in that the first high molecularweight branched carbonate polymer component is thermally stable at a temperature at least 100°C above the Tg of the carbonate polymer blend composition. 2. A carbonate polymer blend composition according to Claim 1 wherein the first high molecular weight branched carbonate polymer component has a weight average molecular weight of at least 3 ti mes that of the second carbonate polymer component. 3. A carbonate polymer blend composition according to Claim 1 comprising from 1 to 35 weight percent high molecular weight branched carbonate polymer component based on weight of first and second components. 4. A carbonate polymer blend composition according to Claim 1 wherein the first carbonate polymer component is prepared from a precursor component comprising a carbonate polymer having one or more latently reactive moieties capable of forming a high molecularweight branched carbonate polymer upon heat activation. 5. An intermediate carbonate polymer blend composition comprising a precursor component having one or more latently reactive moieties capable of forming a high molecular weight branched carbonate polymer upon heat activation and a second, different carbonate polymer component having a lower molecular weight than the high molecular weight branched component, which intermediate blend composition upon heat activation, forms a carbonate polymer blend composition comprising a first high molecular weight branched carbonate polymer component and a second, different carbonate polymer component having a lower molecular weight than the first component, characterized in that the first high molecular weight branched carbonate polymer component is thermally stable at a temperature at least 100 C C above the Tg of the carbonate polymer blend composition. 6. A carbonate polymer blend composition according to Claims 1 or 5 wherein the second carbonate polymer component comprises all or part recycle, regrind and/or scrap carbonate polymer. 7. An improved process for preparing a blend of a first, high molecular weight branched carbonate polymer component and a second, lower molecular weight carbonate polymer component different from the first carbonate polymer component comprising the steps of (a) preparing a precursor component capable of forming the first high molecular weight branched carbonate polymer component, said precursor component comprising a carbonate polymer containing latent thermally activated reactive moieties; (b) combining the precursor component with the second carbonate polymer; and (c) thermally activating the latently reactive moieties of the precursor component to provide a generally homogeneous carbonate polymer blend composition. 8. An improved process for preparing a carbonate polymer blend composition according to Claim 7 where, in step (b), the precursor component is combined with the second carbonate polymer component by (1) dry blending or dual feeding the precursor component with the second, lower molecular weight carbonate polymer component and then (2) melt blending the precursor and second components at a temperature and for a time less than sufficient to significantly thermally activate the latently thermally reactive moieties and (3) recovering an intermediate carbonate polymer blend composition comprising a precursor component having one or more latently reactive moieties capable of forming a high molecular weight branched carbonate polymer component upon heat activation and a second, different carbonate polymer component having a lower molecular weight than the high molecular weight branched component. 9. An ignition resistant, carbonate polymer blend composition comprising, as a first component, a carbonate polymer drip reducing additive selected from the group consisting of a high molecular weight branched carbonate polymer and a carbonate polymer having one or more latently reactive moieties capable of forming a high molecular weight branched carbonate polymer upon heat activation under ignition conditions; as a second component, a second different carbonate polymer component; and, as an optional third component, other ignition resistance additives, wherein the ignition resistance of the blend composition, when tested according to UL 94 attains at least a V-0 rating at 1/8 inch (3.175 mm) or is more ignition resistant. 10. An ignition resistant, transparent carbonate polymer blend composition according to Claim 9. 1 1. An ignition resistant, carbonate polymer blend composition according to Claim 9 wherein the carbonate polymer drip reducing additive is a high molecular weight branched carbonate polymer. 12. A shaped article prepared from a carbonate polymer blend composition according to Claims 1 , 4, 9 or 10.

Inventors: LAUGHNER MICHAEL K, MARKS MAURICE J, LAUGHNER, MICHAEL, K., MARKS, MAURICE, J.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1994
Main classification: C08L69
IPC codes: C08G64, C08L69